Jaroslaw Mikula

The article contains a description of the design solutions proposed by the authors for a hybrid wind turbine bearing, in which the sliding part takes over the load to the turbine shaft after reaching the shaft rotation speed, ensuring hydrodynamic lubrication of the plain bearing and relieving the rolling bearing. This allows for low starting resistance of the power plant and ensures quiet operation during use. Two conceptual solutions of a hybrid bearing were presented, differing in the shape of the plain bearing journal. A mechanism for automatic switching of the load between a rolling and a plain bearing was developed. A solid simulation model of this mechanism was built in the Autodesk Inventor—Dynamic Simulation software Inventor Professional 2023 environment, and its operation was simulated. The results confirmed the usefulness of using this design in shaft-bearing systems of wind turbines with a vertical axis of rotation. Based on the simulation, the speed at which the thrust roller bearing will be released was determined. Technical parameters of a plain bearing with a spherical journal shape were calculated. The height of the lubrication gap and the shaft rotational speed at which the bearing load capacity index reaches a critical value were determined.

The present paper considers the beneficial effects that can be obtained by cold work type of machining performed as the final technological treatment in the process of gears manufacturing. Limitations in the use of shot blasting as a method of surface cold work of gears were pointed out and the concepts of two devices for carrying out the cold work with much greater efficiency than in the case of shot blasting were presented. The discussed devices use pressure burnishing of the critical zones of the gears.

This paper presents the idea of economical, proconsumer hydro power unit. The described hydro power unit allows the generating of electric energy for own needs. However, the overproduction of power can be supplied to the state energy system. The hydropower units of small output that use the local rivers and creeks should additionally support the operation of wind power units. The design of such units should consider such restriction as, among others, cyclic operation that is characterized by often starts and stops. Proconsumer hydropower units have to assure a fast start, respective energy efficiency and a very high durability. These features can be obtained by means of proper design of the journal bearing of turbine main shaft. Hybrid bearing system connecting the journal bearing with the rolling bearing assures the decrease in the start power losses, good durability and reliability of proposed system of hydropower unit. Very important feature of this system is the application of the rolling bearing during the operation. Such bearing allows the decrease in the start time and protects against an insufficient load capacity of lubricating oil film. It is possible to apply the emulsions oil-water as well as clean water as lubricant, too.

The article includes research results for the functional properties achieved for a wide range of sintered tool materials, including sintered carbides, cermets and three types of Al₂O₃ oxide tool ceramics ((Al₂O₃ + ZrO₂, Al₂O₃ + TiC and Al₂O₃ + SiC_(w)) with (Ti,Al)N coating deposited in the cathodic arc evaporation (CAE-PVD) method and comparison with uncoated tool materials. For all coated samples, a uniform wear pattern on tool shank was observed during metallographic analysis. Based on the scanning electron microscope (SEM) metallographic analysis, it was found that the most common types of tribological defects identified in tested materials are: mechanical defects and abrasive wear of the tool side, crater formation on the tool face, cracks on the tool side, chipping on the cutting edge and built-up edge from chip fragments. Deposition of (Ti,Al)N coating on all tested substrates increases the wear resistance and also limits the exceeding of critical levels of permanent stresses. It even increases the tool life many times over. Such a significant increase in tool life results, among other things, from a large increase in microhardness of PVD coated materials compared to uncoated samples, increased resistance to thermal and chemical abrasion, improved chip formation and removal process conditions. Use of hard coatings applied to sintered tool materials is considered to be one of the most important achievements in improving the functional properties of cutting tools and can still be developed by improving the coating structure solutions (sorted and nanocrystalline structures) and extending the range of coating applications (Ti,Al)N in a variety of substrates.

On the basis of dielectric measurements performed in a wide temperature range (173–373 K), a comprehensive analysis of the dielectric and electrical properties of magnetite nanoparticles electrical conduction mechanism of compressed spherical shaped Fe₃O₄ nanoparticles was proposed. The electrical conductivity of Fe₃O₄ nanoparticles was related to two different mechanisms (correlated barrier hopping and non-overlapping small polaron tunneling mechanisms); the transition between them was smooth. Additionally, role of grains and grain boundaries with charge carrier mobility and with observed hopping mechanism was described in detail. It has been confirmed that conductivity dispersion (as a function of frequencies) is closely related to both the long-range mobility (conduction mechanism associated with grain boundaries) and to the short-range mobility (conduction mechanism associated with grains). Calculated electron mobility increases with temperature, which is related to the decreasing value of hopping energy for the tunneling of small polarons. The opposite scenario was observed for the value of electron hopping energy.

This paper presents the evaluation of the service life of dissimilar repair welded joint from Cr-Mo/Cr-Mo-V steel after 200,000 h service under creep condition. The investigations of microstructure using scanning electron microscopy, investigations of mechanical properties at room and elevated temperature as well as creep tests of the basic material from Cr-Mo and Cr-Mo-V steel and welded joint from these steels were carried out. The investigations allowed the time of further safe operation of the repair welded joint in relation to the residual life of the materials to be determined. The evaluation of residual life and disposable residual life, and thus the estimation or determination of possible time of further safe operation, is crucial when the elements are operated much beyond the design work time.